﻿VEETEBEATES. 
  181 
  

  

  into 
  the 
  border 
  of 
  the 
  narrow 
  alate 
  expansion. 
  Surface 
  structure 
  

   minutely 
  and 
  densely 
  punctate 
  ; 
  in 
  the 
  less 
  abraded 
  areas, 
  especially 
  

   toward 
  the 
  inner 
  margin, 
  the 
  punctse 
  are 
  arranged 
  in 
  more 
  or 
  less 
  

   regular 
  parallel 
  transverse 
  lines, 
  conforming 
  in 
  direction 
  to 
  the 
  course 
  

   of 
  the 
  inner 
  margin. 
  This 
  latter 
  feature, 
  however, 
  is 
  seldom 
  ob- 
  

   served 
  to 
  extend 
  over 
  any 
  considerable 
  area 
  of 
  the 
  coronal 
  region, 
  

   which 
  oftener 
  shows 
  the 
  ordinary 
  punctate 
  structure 
  with 
  only 
  faint 
  

   traces 
  of 
  the 
  transverse 
  striation 
  alluded 
  to. 
  Length 
  of 
  a 
  medium- 
  

   size 
  tooth 
  along 
  the 
  antero-lateral 
  border, 
  10 
  mm. 
  ; 
  breadth 
  at 
  inner 
  

   margin, 
  4.5 
  mm.; 
  elevation 
  of 
  antero-lateral 
  border, 
  1.5 
  mm. 
  

  

  The 
  collections 
  afford 
  but 
  few 
  examples 
  of 
  the 
  present 
  species, 
  

   amongst 
  which 
  occur 
  no 
  examples 
  of 
  the 
  broad 
  alate 
  form 
  attribut- 
  

   able 
  to 
  the 
  terminal 
  form 
  of 
  the 
  mandible. 
  Compared 
  with 
  the 
  

   Chester 
  species, 
  Xystrodus 
  verus, 
  it 
  is 
  distinguished 
  by 
  the 
  propor- 
  

   tionately 
  greater 
  breadth, 
  generally 
  smaller 
  size, 
  and 
  the 
  less 
  pre- 
  

   valent 
  and 
  distinct 
  transverse 
  disposition 
  of 
  the 
  punctae 
  of 
  the 
  coronal 
  

   surface. 
  In 
  proportions 
  and 
  general 
  outline, 
  the 
  species 
  bears 
  strik- 
  

   ing 
  resemblance 
  to 
  the 
  corresponding 
  form 
  of 
  X. 
  striatus, 
  Agass., 
  of 
  

   the 
  Mountain 
  limestone, 
  Armagh, 
  but 
  it 
  differs 
  in 
  being 
  smaller 
  and 
  

   in 
  the 
  less 
  marked 
  transverse 
  striation. 
  

  

  Geological 
  position 
  and 
  localities: 
  St. 
  Louis 
  formation; 
  St. 
  Louis 
  

   (Missouri) 
  ; 
  Alton, 
  and 
  Monroe 
  county 
  (Illinois), 
  and 
  Pella 
  (Iowa). 
  

  

  Xystrodus 
  verus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  VIII, 
  Pig. 
  6, 
  7. 
  

  

  Maxillary 
  posterior 
  teeth 
  cuneiform, 
  moderately 
  arched 
  from 
  with- 
  

   in 
  outward. 
  Antero-lateral 
  border 
  with 
  slight 
  sigmoidal 
  curvature, 
  

   abruptly 
  beveled 
  from 
  the 
  coronal 
  angulation, 
  which 
  is 
  obtuse 
  in 
  

   the 
  region 
  of 
  the 
  inner 
  margin 
  and 
  more 
  acute 
  toward 
  the 
  outer 
  

   extremity, 
  probably 
  in 
  consequence 
  of 
  the 
  wearing 
  down 
  of 
  the 
  tri- 
  

   turating 
  surface, 
  articular 
  border, 
  comprising 
  three-fourths 
  the 
  extent 
  

   of 
  this 
  side, 
  the 
  upper 
  portion 
  enveloped 
  in 
  the 
  well-defined 
  enamel 
  

   fold, 
  basal 
  border 
  terminating 
  interiorly 
  in 
  the 
  thin 
  compressed 
  rim 
  ; 
  

   inner 
  margin 
  broadly 
  rounded 
  at 
  the 
  base 
  of 
  the 
  coronal 
  prominence 
  

   and 
  gently 
  deflected 
  backward 
  to 
  the 
  posterior 
  angle 
  of 
  the 
  moderately 
  

   produced 
  alation 
  ; 
  postero-lateral 
  border 
  slightly 
  curved, 
  very 
  gradu- 
  

   ally 
  converging 
  toward 
  outer 
  extremity, 
  coronal 
  enamel 
  forming 
  a 
  

   narrow 
  fold, 
  inbeveled 
  and 
  well 
  defined 
  from 
  the 
  abrupt 
  downward 
  

   and 
  slightly 
  outward 
  projecting 
  basal 
  portion. 
  Coronal 
  surface 
  oc- 
  

   cupied 
  by 
  a 
  broad 
  anterior 
  prominence, 
  slightly 
  arched 
  transverse- 
  

  

  